1. Field of the Invention
The present invention relates to a suction system for an internal combustion engine which has an elbow tube through which the air cleaned by an air cleaner is supplied to a carbureter, and which is suitable for use in portable power working machines such as a chain saw.
2. Description of the Prior Art
In a chain saw of the type which employs, for example, an internal combustion engine as a power source, as it is necessary for its size to be as small as possible, an air cleaner and a carbureter are disposed very close to each other and are coupled with each other by means of an elbow tube having a specific construction, thereby preventing an air-fuel mixture which could soil the air cleaner from blowing back to the air cleaner from the carbureter due to the back pressure of the internal combustion engine.
The elbow tube employed in the conventional chain saw, like the one used in the chain saw disclosed in the specification of Japanese Utility Model Laid-Open No. 120265/1985, has one end coupled with the inlet of the carbureter and the other end bent upward, the distal end of this bent end portion being coupled with the outlet of the air cleaner. The air-fuel mixture that is blown back from the inlet of the carbureter is made to collide with the inner surface of the bent portion, thereby preventing it from reaching the air cleaner.
With such an elbow tube arrangement, however, it is difficult to completely prevent the air-fuel mixture from flowing into the interior of the air cleaner. The air-fuel mixture which has blown back from the carbureter soils the air cleaner, and this can be a cause of lowering the air feeding efficiency or of clogging the air cleaner.